The progression of technology allowing ordnance engineers to improve warheads has often been constrained by metallurgical limitations. Most warhead development prior to the 1980s was based on ordnance engineers finding a precise combination of metallurgy and explosive that delivered good fragmentation. Metals used in ordnance typically exhibit properties of high yield strength across most operational temperature ranges. The use of specialized steels frequently requires vendors to acquire batches of low usage steel from a selective group of US steel mills. During the cold war era, when the US planned for large volume purchases and ammunition, the sustainment of war stocks necessitated reliance on this supply chain paradigm. Often further heat treating, knurling and forming of metals have been used in warheads to further optimize fragmentation. A good example of the matching of specified steel and explosives is the US M430 40 mm cartridge that uses a specific steel, production processes and heat treatment specifications to produce the required fragmentation. One should note that this combination of precision metallurgy and choice of explosive often remains a best value solution as exemplified by the US Air Force (USAF) recent decision to specify a high yield strength ES-1 steel to be used in USAF ordnance. There are significant advantages to metal body warheads but one must also recognize that when using natural fragmentation (1) a proportion of the metal is transformed into very small fragments (or dust) which is ineffective when trying to defeat both anti materiel and antipersonnel targets, and (2) the formed warhead metal body, without knurling or forming, generally produces a detonation with a wide distribution of fragmenting mass. Scoring or otherwise imparting impressions on warhead steel can improve the distribution of fragment mass resulting from a detonation, but lethally effective fragmenting mass is still lost in the process of detonation.
DPICM and UXO:
The US Artillery Corps in the 1970s selected the Dual-Purpose Improved Conventional Munition (DPICM) as the principal ordnance in rocket and large caliber projectile warheads to defeat anti materiel and antipersonnel targets. The US produced large volumes of DPICM 155 mm artillery projectiles and rockets. The DPICM purchases required high volume production of bomblets. These bomblets employed natural fragmentation grenades that also incorporated conical shape charges to improve their anti materiel capability. Unfortunately, the high dud rate of DPICM, which incorporated numerous sub-munitions, gave rise to enormous clean-up costs after the First Gulf War. Subsequent use exhibited high dud rates in certain Middle East conflicts and led to many countries agreeing to ban DPICM technology (see the Dublin Convention on Cluster Munitions). With DPICM as their principal projectile, the US Artillery Corps found itself sidelined in much of the Iraq conflict as their DPICM artillery shells created too much collateral damage and too much UXO to be used in the vicinity of Iraqi population centers.
Medium Caliber Use of Preformed Fragmented Warheads:
As we entered the twentieth century, one sees increasing use of pre-fragmentation, and these pre-fragmentation architectures were being introduced into many military products. Many patents were awarded depicting unique combinations of warheads as prominent ordnance companies began to utilize pre-fragmenting bodies. The German company Diehl incorporated pre-fragmented wire and spheres encased in resin that produced an effective medium caliber warhead assembly that US SOCOM incorporated into NAMMO's MK285 cartridge. The Oerlikon company in Switzerland developed a medium caliber AHEAD warhead that optimized performance in ground-to-air applications. This technology was fielded with the Danish and Dutch Armies in a 35 mm weapon system. Nevertheless, it must be recognized that the vast preponderance of US produced medium caliber munitions relied on the solutions pioneered in the 1970s.
Large Caliber Use of Preformed Fragmented Warheads:
The South African company Denel developed and later, after formation of Rheinmetall Denel Munitions (Phy) Ltd (RDM), produced an effective artillery shell where preformed fragments (PFF) are encased within two metal cones forming the body of a unitary high explosive artillery projectile. Having a need to field a new unitary projectile that minimized collateral damage while defeating two target sets, the US Government contracted with General Dynamics to import this product from South Africa. In the last few years, this 105 mm High Explosive Preformed Fragments (HE-PFF) projectile has been qualified as the US M1130 105 mm Artillery Shell. While the US government obtained data rights for this South African designed projectile, no US producer manufactures the projectile's components and the US production base is not organized to produce this product. A cutaway of the “XM1130” projectile was publically exhibited for three days in Washington D.C., 10-12 Oct. 2011, in the General Dynamics (GD) booth at the Annual United States Army Association Meeting and Show. The 2011 GD display showed a cross section cutaway model of the XM1130 warhead with preformed fragments in a conical formation wedged within two projectile bodies. The warhead uses both natural fragmenting bodies and spherical metal preformed fragments that delivered a bimodal distribution of fragments upon detonation. In the realm of Artillery, therefore, South African ordnance designers have pioneered the science of combining pre-fragmentation with naturally fragmenting metal bodies to produce a bimodal fragment distribution. This bimodal distribution was attractive to the United States Army after the Army (1) analyzed target sets, and (2) decided that the use of a unitary warhead was the best overall design to meet user requirements. With this artillery hardware imported from South Africa and with the challenging task of organizing cost effective production within the US National Technical Industrial Base (NTIB) it remains unclear how this technology will be economically transitioned into the United States.
Utility of Flow Forming Production Technology:
Flow forming of metal bodies began to be utilized in the production of US ordnance in the 1990s. This flow forming process progressively moves metal or blended metals into cylindrical forms with a dense and sturdy metallurgy. To date, most use of flow forming of ordnance since the 1990s has been in the production of rocket motor cases. It is noteworthy that this production process can produce high strength, thin walled cylindrical or conical metal shapes with minimal tolerance variation. The flow forming process can produce complex geometries provided those geometries can be formed on a mandrel.
Liners:
In the last decade the US Army Research Development and Engineering Center (ARDEC) has funded developmental advances in the use of liners or sleeves to mitigate impact threats as determined by Insensitive Munitions (IM) testing.
Notable Prior Art (Patents):
There is a plethora of prior art in scoring and embossing of metal plates and fragmentary components. US Navy U.S. Pat. No. 3,566,794 identified how multi-walled warhead casings can be useful to ordnance designers. The UK MOD U.S. Pat. No. 4,398,467 taught the use of notched rods or wire in warheads. The Hughes Aircraft Company U.S. Pat. No. 4,313,890 taught the inclusion of preformed fragments in a tubular outer casing. Rheinmetall's U.S. Pat. No. 4,982,668 taught a fragmenting body with pre-fragmentation on the outer face of the warhead. The US Navy's US Invention Registration No. H1047 taught the use of notched rods to adjust warhead fragmentation. The US Navy U.S. Pat. No. 5,040,464 identifies methods to control a fragmentation mix. The Diehl U.S. Pat. No. 5,979,332 provided a configuration optimizing fragmentation with wire and pre-formed fragments set in a resin. This intellectual property was adopted by US SOCOM and incorporated in the US MK285 Air-Burst Cartridge. Rheinmetall's European Patent EP0433544A1 identified unique and useful casing configurations. Giat's U.S. Pat. No. 6,857,372 taught how the use of scoring on inner and outer projectile bodies can influence the fragmentation of the metal case. The US Army U.S. Pat. No. 7,886,667 taught how the use of liners to produce temporal delays in detonation waves assisting in optimizing the fragmentation of a warhead body.
Notable Prior Art (Published Design Information):
The US Navy Air Warfare Center Weapons Division pioneered methods of controlled fragmentation known as the “Person V-notch” in the 1960s and these methods were recently incorporated by the Russians into their 122 mm GRAD 9M22U warhead body. The company PRETIS in Bosnia Herzegovina has also incorporated the US Navy method into their 128 mm M777 product. Bofors 40/57 mm 3P (Pre-fragmented Programmable Proximity) ammunition, introduced to the market in the late 1990s, incorporated preformed fragments encased in two metal bodies. Diehl DM261A2 (HE-PFF) also includes an interesting design of encased preformed fragments within a metal body. One should note that the US Marine Corps developed an interest in the Saab (formerly Ruag Switzerland) MAPAM mortar technology buying test samples that delivered impressive, reliable fragmentation. It should also be recognized that some warhead designs are unpublished because of national security sensitivities. As previously discussed, the RDM M1130 warhead design with preformed fragments is useful validating prior art and providing an example of a warhead with a bimodal distribution of fragments. The concept disclosed herein is an alternative to RDM's disclosed prior art.
Target Defeat Analysis and Terminal Effects:
The mechanics of good ordnance engineering and design start with the analysis of targets and terminal effects. Targets frequently are susceptible to damage from the impact of fragments with certain size, mass and energy but target sets must be analyzed based on realistic situations. For example, an upright soldier in a uniform may be highly susceptible to incapacitation by fragments of various sizes traveling at a high velocity. By contrast the soldier wearing a flak jacket and helmet positioned in a bunker, may be almost invulnerable to incapacitation if (1) the fragments are too small and (2) the density or spray of fragments are too low. Moreover, the small irregular fragments normally produced by the natural fragmentation of warhead bodies may not retain good ballistic flight characteristics or uniform size so these fragments may not penetrate enemy flak jackets or helmets. Flak jackets and helmets can certainly be defeated by fragments with adequate velocity, mass and ballistic characteristics. Accordingly, a target analysis, in a realistic combat situation may indicate that a distinct bimodal fragment distribution size can provide a better optimized terminal effect to defeat a particular set of targets.
Optimizing Larger Warheads:
An obvious challenge emerges as the US Army begins development of its next generation unitary artillery warheads. The Army does not have the financial resources to restart a Crusader type program so it will continue to use the M109 Paladin and M777 series 155 mm×39 caliber shells, adding rocket assisted projectiles (RAP), base bleed technology and precision guidance. Precision guidance kits (PGK) have been perfected and provide precision and flight course adjustment offsetting the errors resulting from RAP and base bleed propulsion. The use of RAP or base bleed technology inevitably reduces the warhead weight relative to the overall projectile weight. In this situation there is obvious pressure on ordnance designers to optimize fragment effects on targets. Since military users also desire a reduction in collateral damage incidents, where militaries intend to destroy targets that are in close proximity to non-combatants, ordnance engineers must find designs that reliably and repeatedly fragment a warhead such that the target is incapacitated while minimizing the throw of fragments beyond the intended terminal effect zone.
Optimizing Medium Caliber and Air Bursting Fragmenting Warheads:
Medium caliber warheads have significantly less weight than larger tank, mortar and artillery warheads. Medium caliber ammunition designers must therefore devise novel approaches to optimize warhead body fragmentation. Moreover, US and NATO forces are now demanding the ability to kill targets in defilade. In the generally accepted systems approach, defeating targets in defilade with medium caliber ammunition will continue to use time fuzes and fire control devices of the type pioneered by US SOCOM when they adopted GD's MK47 weapon system firing NAMMO MK285 ammunition.
Fragment Throw and Collateral Damage:
Ammunition relying solely on natural fragmentation from the warhead body inevitably generates fragments of widely varying mass distribution. The introduction of notching, scoring, knurling or other techniques can produce fragments with less variation but fragments may still retain significant size and energy or fragments may be both undersized and oversized. Undersized fragments have minimal terminal effect. Oversized targets generally can prove dangerous and produce collateral damage beyond the desired terminal effect zone as large fragments are ejected with more energy at long distances from their impact point. These larger fragments, with significant impact energy, can kill and injure non-combatants far from the impact point. In the era of precision strikes, the mass destruction typically caused on targets by artillery is problematic and can infringe on accepted standards of modern warfare. Hence, modern ordnance engineers strive to insure that the fragment size and velocity produced at detonation (1) successfully defeat the desired targets while (2) precluding collateral damage beyond the intended target or target set. The reliable creation of fragments (density, size and velocity) with specified mass range is desired. Further, in many cases a reliable bimodal distribution of fragments is required to impart a desired terminal effect on two target sets while minimizing collateral damage.
Fragment Shape and Velocity:
The natural fragmentation arising from the detonation of warhead bodies produces fragments with irregular shapes and irregular surfaces. These fragments are propelled by the expanding gases forming multiple shockwaves as the fragments travel beyond the sound barrier. These irregular shapes and surfaces induce drag and turbulence about the fragments which rapidly degrade the velocity and range of these “natural” fragments. Preformed fragments, particularly spheres, by contrast have aerodynamically smoother surfaces that provide better ballistic flight (reduced drag) from the detonation point.
Fragment Throw and Safe Separation:
Further, when using high velocity cartridges, such as 30 mm×173 ammunition, the forward speed of the projectile may inhibit the effectiveness of high speed “rearward” fragments. By contrast, lower velocity ammunition such as 40 mm×53 projectiles travel slow enough to propel fragments rearward, such that the fragments can still effectively defeat targets. The ejection of fragments at right angles to the flight path for medium caliber ammunition represents an optimum defilade kill geometry. A medium caliber cartridge must meet the safe separation safety requirements for a system. As an example, the US M430 cartridge exhibits inadequate safe separation. Hence, the Army must train gunners using MK19s (40 mm AGL) to never fire at targets less than 300 meters away unless the commander deems it acceptable to expose friendly forces to rearward fragments of the M430 cartridge. US SOCOM has adopted the MK285 cartridge from the MK47 (40 mm AGL) with a safe separation distance of less than 100 meters. This improved safe separation of the MK285 cartridge allows US SOF forces to engage enemy targets at shorter ranges relative to their US Army counterparts. Where a warhead designer is able to design warheads that reliably fragment and throw fragments rearward where these fragments are of a limited size and mass, such a projectile will have optimized safe separation from the gunner. Stated another way, where a warhead does not produce heavy high velocity fragments thrown rearward, that warhead will have a better optimized safe separation allowing friendly forces to use weapons at closer range.
The prior art incorporated into most US designs was developed in the 1970s. In an age of air burst munitions, precision time fuzes, Insensitive Munitions (IM) Technologies and Precision Guidance Kits the continued use of older “metal-explosive warheads” has the downside that the technique generally creates a wide distribution of fragmenting mass without distinct nodes. Many fragments generated by natural fragmentation of warhead bodies are produced in a mass range (and with kinetic energy) that lacks effect on targets and produces an unacceptable danger of collateral damage.
Summary:
The referenced fielded US projectiles discussed in this patent application are warheads used in gun fired ammunition. Warheads are also widely utilized in missiles and rockets. The warheads for missiles have different design constraints. Gun fired warheads, especially those that are spin stabilized, must undergo high setback forces and require adequate gyroscopic stability. Missiles and rockets have other different and demanding design requirements.
At this crossroads in the history of military technology, there is a need to provide novel warhead designs that (1)(a) reliably produce bimodal or (b) multimodal fragment distribution, with (c) a correspondingly optimized terminal effect on a target or target set, that also (2)(a) minimize collateral damage and (b) deliver adequate safe separation.